Our ability to measure directly the forces between macromolecules or between membrane surfaces has made us aware of two main features (a) In the important last few nanometers where molecules approach contact, interaction is dominated by the work of removal of water solvent from their surfaces; (b) At larger distances macromolecules or membranes move or undulate to repel by the "steric" action of colliding molecules. Both these kinds of forces can be expected to act inside a biological cell whose functioning units are assemblies of molecules or membranes in continuous and controlled reorganization. . One is to provide information for a more correct theoretical description of molecular interaction and assembly. . A second use of the data is to see how the measured forces act at the functional level of, say, controlling the contact and fusion of membranes as in a secretory process, or determining the packing of DNA or other long molecules, or perturbing the rearrangements of protein structure that effect the "gating" of trans-membrane ionic channels, or even affect the activity of enzymes whose function depends on particular forms of packing components. (We have been carrying out work on each of these processes.) . Third, we see the possibility of introducing measured force and motion information into molecular dynamics algorithms, to bring the benefit of this information to the active but still relatively formal area of computer simulation.